According to one aspect of the invention, this invention relates to sintering of a silicon nitride article by employing at least one carbon-containing layer closely adjacent to the article and at least one ceramic-containing layer intermediate to the article and carbon-containing layer. According to another aspect, the invention relates to the combination of such layers and the silicon nitride article.
Heretofore, difficulties are many times encountered in the sintering of silicon nitride articles at lower pressures of, for example, less than 200 psig, and particularly at pressures near atmospheric pressure. The primary difficulty is in obtaining an acceptably high density of at least and preferably more than 90 percent of the theoretical density of silicon nitride. It is particularly advantageous to sinter at the above-described pressures rather than at higher pressures to avoid use of complex and expensive equipment associated with operation at high pressures.